Parking assistance device

ABSTRACT

A parking assist device according to the present invention includes a backward-direction-path calculation unit that calculates a backward-direction path for taking an own vehicle out from a target parking position B based on constraint conditions of a parking space and an own-vehicle behavior, a connection-candidate-position storage unit that sets a plurality of connection candidate positions D on the backward-direction path, a forward-direction-path calculation unit that calculates a forward-direction path leadable to one of the connection candidate positions D from a current position A of the own vehicle, and a parking-path setting unit that sets a parking path by combining the backward-direction path and the forward-direction path.

CROSS REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. patent application Ser. No.15/770,672, filed Apr. 24, 2018, which claims priority to JP PatentApplication No. 2015-211322 filed on Oct. 27, 2015 and PCT/JP2016/075466filed on Aug. 31, 2016, which is/are incorporated by reference as iffully set forth.

TECHNICAL FIELD

The present invention relates to a parking assist device for vehicles.

BACKGROUND ART

PTL 1 discloses a technique of a parking assist device that calculates aguide path including turns to park a vehicle and assists the vehicle toreach a target position along the guide path.

CITATION LIST Patent Literature

PTL 1: JP 2010-208392 A

SUMMARY OF INVENTION Technical Problem

In the technique disclosed in PTL 1, since a guide path is calculatedbased on the positional relation between an initial position at whichparking assistance is started and a target parking position and therelation of a vehicle posture, it is impossible to perform parkingassistance in the case of, for example, a place where the target parkingposition cannot be guided from the initial position of the vehicle.

The present invention has been made in view of the above, and is toprovide a parking assist device that calculates a parking path includingturns for guiding a vehicle to a target parking position withoutdepending on an initial position at which parking assist is started andon a vehicle posture, and to park the vehicle at a parking positiondesired by a driver with a proper vehicle posture.

Solution to Problem

A parking assist device according to the present invention for solvingthe above problem is a parking assist device that calculates a parkingpath from a current position of an own vehicle to a target parkingposition, the parking assist device including a backward-direction-pathcalculation unit that calculates a backward-direction path for takingthe own vehicle out from the target parking position based on constraintconditions of a parking space and an own-vehicle behavior, aconnection-candidate-position storage unit that sets a plurality ofconnection candidate positions on the backward-direction path, aforward-direction-path calculation unit that calculates aforward-direction path leadable to one of the plurality of connectioncandidate positions from the current position of the own vehicle, and aparking-path setting unit that sets the parking path by combining thebackward-direction path and the forward-direction path.

Advantageous Effects of Invention

According to the present invention, it is possible to calculate aparking path including turns for guiding a vehicle to a target parkingposition without depending on an initial position at which parkingassist is started and on a vehicle posture, and to park the vehicle at aparking position desired by a driver with a proper vehicle posture. Notethat, problems, configurations, and effects other than those describedabove will be clarified from the following description of an embodiment.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a functional block diagram of a parking assist deviceaccording to an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a method for calculating abackward-direction path for backward parallel parking.

FIG. 3 is a diagram showing an example of a method for calculating abackward-direction path for forward parallel parking.

FIG. 4 is a diagram showing connection candidate positions on abackward-direction path in the case of backward parallel parking.

FIG. 5 is a diagram showing connection candidate positions on abackward-direction path in the case of forward parallel parking.

FIG. 6 is a flowchart explaining a method for calculating connectioncandidate positions on a backward-direction path.

FIG. 7 is a processing flow of reachability determination.

FIG. 8A is a diagram explaining an example of reachability determinationby one-side steering.

FIG. 8B is a diagram explaining an example of reachability determinationby one-side steering.

FIG. 8C is a diagram explaining an example of reachability determinationby one-side steering.

FIG. 8D is a diagram explaining an example of reachability determinationby S-shaped steering.

FIG. 8E is a diagram explaining an example of reachability determinationby S-shaped steering.

FIG. 9 is a diagram explaining a method for generating aforward-direction path by one-side steering.

FIG. 10 is a diagram explaining a method for generating aforward-direction path by S-shaped steering.

FIG. 11 is a diagram explaining a method for generating aforward-direction path by S-shaped steering.

FIG. 12 is a diagram explaining a method for generating aforward-direction path by S-shaped steering.

DESCRIPTION OF EMBODIMENTS

Next, an embodiment of the present invention will be described withreference to the drawings.

FIG. 1 is a functional block diagram of a parking assist deviceaccording to an embodiment of the present invention.

A parking assist device 1 of the present invention is to calculate aparking path for guiding an own vehicle from a current position of theown vehicle to a target parking position and to assist parking so thatthe own vehicle moves along the calculated parking path, and is suitablefor assisting parking operation especially in a narrow space where turnsare required twice or more.

The parking assist device 1 includes a backward-direction-pathcalculation unit 11 that calculates a backward-direction path for takingan own vehicle out from a target parking position based on constraintconditions of a parking space and an own-vehicle behavior, aconnection-candidate-position storage unit 12 that sets a plurality ofconnection candidate positions on the backward-direction path, aforward-direction-path calculation unit 13 that calculates aforward-direction path leadable to one of the plurality of connectioncandidate positions from the current position of the own vehicle, and aparking-path setting unit 14 that sets a parking path by combining thebackward-direction path and the forward-direction path.

As shown in FIG. 1, target-parking-space information,target-parking-position information, and own-vehicle information areinput to the backward-direction-path calculation unit 11. Thetarget-parking-space information includes information that is aconstraint condition of the parking space, such as the distances to thesurrounding walls and other vehicles, the target-parking-positioninformation includes information such as the shape of the target parkingposition and the relative position to the own vehicle, and theown-vehicle information includes information that is a constraintcondition of the own-vehicle behavior such as a turning radius of theown vehicle.

Own-vehicle position information is input to the forward-direction-pathcalculation unit 13. Information from an operation input unit 15, suchas a parking frame selected by a user from a plurality of parkingframes, is input to the parking-path setting unit 14. A path displayunit 16 is an in-vehicle monitor that a driver can see in a vehicle, andcan display a parking path by superimposing it on an image from acamera. The driver can park the vehicle at the target parking positionby operating the vehicle according to the parking path displayed on thein-vehicle monitor. Alternatively, the parking assist device 1 mayoutput information on a parking path and automatically operate and parkthe vehicle at the target parking position.

<Backward-Direction-Path Calculation Unit>

The backward-direction-path calculation unit 11 calculates abackward-direction path based on target-parking-space information suchas obstacles around a parking frame, target-parking-position informationsuch as the shape and position of the parking frame, and own-vehicleinformation on a vehicle specification such as the size of an ownvehicle and the minimum turning radius. The target-parking-spaceinformation can be acquired from, for example, a detection signal of anultrasonic sensor mounted on the own vehicle or an image from anin-vehicle camera. Alternatively, infrastructure information of aparking lot may be acquired.

The backward-direction path is a virtual movement path which is anestimated path for taking the own vehicle out from a target parkingposition at which the own vehicle is parked. The backward-direction pathis calculated completely irrelevantly to the current position of the ownvehicle. The backward-direction path includes a plurality of turnpositions at which the own vehicle is switched back and forth.

The backward-direction path is calculated based on the constraintconditions of the parking space and the own-vehicle behavior. Inbackward parallel parking, a path assuming that the own vehicle is tookout in the same direction as the direction of the own vehicle at thecurrent position when the target parking position is set as the originis generated. In forward parallel parking, a backward-direction pathassuming that the own vehicle is took out in the direction opposite tothe direction of the own vehicle at the current position when the targetparking position is set as the origin.

For example, in the case of backward parallel parking in which theposture of a vehicle at the target parking position is directedbackward, a path to a point at which a reference point, which is theintermediate position between the left and right rear wheels of thevehicle (hereinafter, referred to as a reference point), gets out of theparking frame by moving the vehicle straight forward from the targetparking position, an forward path for the own vehicle to reach areachable limit position with respect to a front obstacle by steering soas to take the vehicle out in the same direction as the direction of theown vehicle at the current position and moving forward, and a backwardpath for the own vehicle to reach a reachable limit position withrespect to a rear obstacle by straightening the front wheels withrespect to the own vehicle and moving backward are calculated. Then, thecalculation of the backward-direction path for which the forward pathand the backward path are alternately calculated is performed until apredetermined termination condition is satisfied. The reachable limitposition means a position separated from an obstacle with apredetermined gap therebetween. The predetermined gap has a margintaking an error or the like into consideration so as not to contact withthe obstacle, is preferably to be smaller, and set to, for example,about 1 cm to 50 cm.

On the other hand, in the case of forward parallel parking in which theposture of the own vehicle at the target parking position is directedforward, a path to the point at which the reference point is separatedfrom the parking frame by a predetermined distance by moving the vehiclestraight backward from the target parking position, a backward path forthe own vehicle to reach to a reachable limit position with respect to arear obstacle by steering so as to take the vehicle out in the oppositedirection to the direction of the own vehicle at the current positionand moving backward, and a forward path for the own vehicle to reach areachable limit position with respect to a front obstacle bystraightening the front wheels with respect to the own vehicle andmoving forward are calculated. Then, the calculation of thebackward-direction path for which the forward path and the backward pathare alternately calculated is performed until a predeterminedtermination condition is satisfied.

The backward-direction-path calculation unit 11 calculates abackward-direction path until, as a predetermined termination condition,for example, at least one of a first condition that the direction of theown vehicle on the backward-direction path is 90 degrees with respect tothe direction of the own vehicle at the target parking position, asecond condition that the own vehicle reaches a point separatedlaterally by a predetermined distance Hmax from the target parkingposition, and a third condition that the number of turns on thebackward-direction path reaches a predetermined number is satisfied.

FIGS. 2 and 3 are diagrams showing an example of a method forcalculating a backward-direction path of a vehicle in accordance withpreset conditions; FIG. 2 shows a case of backward parallel parking, andFIG. 3 shows a case of forward parallel parking.

In the backward-direction path, in the example of the backward parallelparking shown in FIG. 2, an own vehicle 21 is moved straight forwardfrom a state (a) in which the own vehicle 21 is parked at the targetparking position in a parking frame S, a reference point 22 of the ownvehicle 21 gets out the parking frame S (b), the own vehicle 21 reachesa reachable limit position with respect to a front obstacle 32 bysteering to the left and moving forward (c), and the own vehicle 21reaches a reachable limit position with respect to a rear obstacle 33 bystraightening the front wheels with respect to the own vehicle at theposition and moving backward (d). Then, the path through the forwardpath by steering to the left (e), the backward path by moving straightbackward (f), the forward path by steering to the left (g), and thebackward path by moving straight backward (h), to the state (i) in whichthe direction of the own vehicle 21 is 90 degrees with respect to thedirection of the own vehicle 21 at the target parking position iscalculated.

Similarly, in the example of the forward parallel parking shown in FIG.3, the own vehicle 21 is moved straight backward from the state (a) inwhich the own vehicle 21 is parked at the target parking position in theparking frame S, the reference point 22 of the own vehicle 21 gets outthe parking frame 31 and reach a position separated from a parking frame31 (b), the own vehicle 21 reaches the reachable limit position withrespect to the rear obstacle 32 by steering to the right and movingbackward (c), and the own vehicle 21 reaches the reachable limitposition with respect to the front obstacle 33 by straightening thefront wheels with respect to the own vehicle 21 at the position andmoving forward (d). Then, the path through the backward path by steeringto the right (e), the forward path by moving straight forward (f), thebackward path by steering to the right (g), and the forward path bymoving straight forward (h), to the state (i) in which the direction ofthe own vehicle is 90 degrees with respect to the direction of the ownvehicle 21 at the target parking position is calculated.

Note that, the method for calculating the backward-direction path is notlimited only to the above method, and the calculation may be performedaccording to other conditions. Alternatively, the calculation may beperformed by selecting a condition suitable for the target parking spacefrom a plurality of preset conditions.

<Connection-Candidate-Position Storage Unit>

The connection-candidate-position storage unit 12 sets a plurality ofconnection candidate lines PL at predetermined intervals on a passage G,and stores positions at which the reference point 22 of the own vehicle21 crosses these connection candidate lines PL on the backward-directionpath and the directions of the own vehicle 21 at the positions asconnection candidate positions D.

FIG. 4 is a diagram showing connection candidate positions on abackward-direction path in the case of backward parallel parking.

The connection candidate lines PLn (n is a numeral) are set so as toextend in the direction of the width of the passage G in front of thetarget parking position B, and are set in the left direction from theparking frame 31 on the passage G at predetermined intervals. In thepresent embodiment, the connection candidate lines PLn are set from 1.5m in the lateral direction setting the target parking position B as areference at intervals of 0.5 m. In addition, information on thepositions at which the reference point 22 passes through the connectioncandidate lines PL on the backward-direction path, and on the directionsof the own vehicle at the positions is stored as a connection candidateposition D. In the drawing, the reference sign A indicates the currentposition, the reference sign B indicates the parking target position,the reference sign C indicates the reachable limit position, and thereference sign E indicates the reaching position.

FIG. 5 is a diagram showing connection candidate positions on abackward-direction path in the case of forward parallel parking.

The connection candidate lines PL are set so as to extend in thedirection of the width of the passage G in front of the target parkingposition B. In the present embodiment, the connection candidate lines PLare set at intervals of 0.5 m along the passage G. In addition,information on the positions at which the reference point 22 passesthrough the connection candidate lines PL on the backward-directionpath, and on the directions of the own vehicle at the positions isstored as a connection candidate position D.

FIG. 6 is a flowchart explaining a method for calculating connectioncandidate positions on a backward-direction path.

First, in accordance with a predetermined rule, calculation forvirtually moving the own vehicle 21 in the direction for taking the ownvehicle 21 out from the target parking position is performed (S101), andwhether the own vehicle 21 collides with an obstacle is determined(S102). When it is determined that the own vehicle 21 collides with theobstacle, a position separated by a predetermined gap in front of thecollision position is determined as the reachable limit position C, andthe gear is shifted so as to switch from moving forward to movingbackward or from moving backward to moving forward (S107).

Then, whether the own vehicle 21 reaches the predetermined connectioncandidate position D is determined (S103), it is determined that the ownvehicle 21 reaches the predetermined connection candidate position Dwhen the reference point 22 of the own vehicle 21 passes through theconnection candidate line PL, and the information on the position atthat time and on the direction of the own vehicle 21 at the position isstored (S108). Then, whether the angle of the own vehicle is 90 degreeswith respect to the parking frame, which is the first condition, isdetermined (S104), it is determined that the first condition issatisfied when the angle is 90 degrees, and the routine is terminated.

On the other hand, when the direction of the own vehicle 21 is not 90degrees, whether the own vehicle 21 is separated by the predetermineddistance Hmax or more is determined (S105). In the present embodiment,the predetermined distance Hmax is set to 7 m. It is determined that thesecond condition is satisfied when the own vehicle 21 is separated bythe predetermined distance Hmax or more, and the routine is terminated.

<Forward-Direction-Path Calculation Unit>

The forward-direction-path calculation unit 13 calculates aforward-direction path that can lead to one of the plurality ofconnection candidate positions D from the current position A of the ownvehicle 21. The forward-direction path is a path that can lead to aconnection candidate position D from the current position of the ownvehicle 21 by either moving forward or backward without switching movingforward and backward. Such calculation is performed based on theown-vehicle position information and the specification information ofthe own vehicle, and the forward-direction path is sequentiallycalculated from a connection candidate position that can be reached witha smaller number of turns and is closer to the current position of theown vehicle. Then, a connection candidate position D that can be reachedfrom the current position of the own vehicle and closest to the ownvehicle is selected, the connection candidate position D is set as thereaching position E, and a forward-direction path from the currentposition A is calculated.

If the own vehicle 21 can be arranged in a predetermined direction at aconnection candidate position on the backward-direction path from thecurrent position, the own vehicle 21 can be moved to the target parkingposition only by following the backward-direction path in the backwarddirection. Thus, the forward-direction-path calculation unit 13 selects,from a plurality of connection candidate positions on thebackward-direction path, a connection candidate position at which thevehicle can be arranged in a predetermined direction from the currentposition. Then, in order to shorten the time required for parking asshort as possible, a connection candidate position having a short movingdistance from the current position is selected.

FIG. 7 is a processing flow of reachability determination.

This processing flow is looped for the number of connection candidatepositions (S111), and, first, whether the own vehicle 21 can reach theconnection candidate position by one-side steering (S112). The one-sidesteering is an operation of steering the steering wheel to either one ofthe left or right side. Then, when it is determined that the own vehicle21 cannot reach the connection candidate position by the one-sidesteering, whether the own vehicle 21 reach the connection candidateposition by S-shaped steering (S116). The S-shaped steering is anoperation of steering the steering wheel to both of the left and rightsides.

Then, when it is determined that the own vehicle 21 can reach theconnection candidate position D by the one-side steering or S-shapedsteering, the connection candidate position D is selected as thereaching position E, and a forward-direction path from the currentposition of the own vehicle 21 to the reaching position E is generated(S113).

Then, whether the own vehicle 21 contacts with an obstacle on theforward-direction path is determined (S114), when it is determined thatthe own vehicle 21 does contact, a connection OK flag is set to ON, thegenerated forward-direction path is stored, and the loop is terminated(S117). On the other hand, when it is determined that the own vehicle 21cannot reach the connection candidate position by the one-side steeringor S-shaped steering (NO in S112 and S116), or when it is determinedthat the own vehicle 21 contacts in the contact determination (YES inS114), the determination on the connection candidate position D isterminated, and determination for the remaining connection candidatepositions is performed. When it is determined that the own vehicle 21cannot reach all of the connection candidate positions D, the connectionOK flag is set to OFF (S115), and the processing flow is terminated.

FIGS. 8A to 8C are diagrams explaining an example of reachabilitydetermination by one-side steering, and FIGS. 8D and 8E are diagrams forexplaining an example of reachability determination by S-shapedsteering.

In the reachability determination by one-side steering in S112, it isdetermined that the own vehicle 21 can reach the connection candidateposition when all the following conditions (a1) to (a3) are satisfied(the angular difference and position are also restricted).

(a1) An axis line A2 at the current position A of the own vehicle 21 andan axis line E2 at the reaching position E cross.

(a2) A turning circle A1 at the current position A and the axis line E2at the reaching position E do not cross.

(a3) A turning circle E1 at the reaching position E and the axis line A2at the current position A do not cross.

The turning circle is assumed to be a circular arc (minimum rotationlocus) on the turning side taking the clothoid into consideration.

In the example shown in FIG. 8A, since the axis lines A2 and E2 cross ata crossing position F1, the above condition (a1) is satisfied. Thus, itis determined that the own vehicle 21 can reach the connection candidateposition by one-side steering. On the other hand, in FIG. 8B, since theturning circle E1 and the axis line A2 at the current position cross,the above condition (a3) is not satisfied. In the example shown in FIG.8C, since the turning circle A1 at the current position and the axisline E2 at the reaching position E cross, the above condition (a2) isnot satisfied. Thus, in the example shown in FIGS. 8B and 8C, it isdetermined that the own vehicle 21 cannot reach the connection candidateposition by one-side steering, and the determination as to whetherS-shaped steering is possible is performed.

In the reachability determination by S-shaped steering in S116, it isdetermined that the own vehicle 21 can reach the connection candidateposition when the following condition (a4) is satisfied (the angulardifference and position are also restricted).

(a4) The turning circle A1 at the current position A and the turningcircle E1 at the reaching position E do not cross.

In the example shown in FIG. 8D, since the turning circle A1 and theturning circle E1 do not cross, the condition is satisfied. Thus, it isdetermined that the own vehicle 21 can reach the connection candidateposition by S-shaped steering. On the other hand, in the example shownin FIG. 8E, since the turning circle A1 and the turning circle E1 cross,the condition is not satisfied, and it is determined that the ownvehicle 21 cannot reach the connection candidate position by S-shapedturning.

FIG. 9 is a diagram explaining a method for generating aforward-direction path by one-side steering.

In order to generate a path by one-side steering from the currentposition A to the reaching position E, first, as shown in FIG. 9(a), adistance Ls between a crossing K of the axis lines A2 and E2 and thecurrent position A, and a distance Le between the crossing K and thereaching position E are calculated, and the shorter distance is selected(in the example shown in the drawing, the distance Le is selected).Then, as shown in FIG. 9(b), a circle having two axis lines A2 and E2 ascommon tangents and passing through a position separated by the shorterdistance from the crossing K is drawn, and the radius R is calculatedwith the following expression (1) from the geometric calculation.

$\begin{matrix}{\left\lbrack {{Expression}\mspace{14mu} 1} \right\rbrack\mspace{580mu}} & \; \\{R = \frac{L_{c}}{\tan\;\frac{\theta}{2}}} & (1)\end{matrix}$

In this manner, it is possible to generate a forward-direction pathcombining a straight line and an arc.

FIG. 10 is a diagram explaining a method for generating aforward-direction path by S-shaped steering, and is a diagram explaininga generation method when the axis line E2 does not cross with the Xaxis, which is the axis line E2 at the current position A, behind thereaching position E.

Here, the radius R of common circles having the same radius iscalculated to draw an S-shape. As long as a contact point of the circleis obtained, an S-shaped forward-direction path can be generated bycombining the arc of the turning circle A1 and the arc of the turningcircle E1.

The radius of the common circle is obtained from the distance betweenthe center coordinates since the center coordinates of the circles areobtained.

$\begin{matrix}{\left\lbrack {{Expression}\mspace{14mu} 2} \right\rbrack\mspace{580mu}} & \; \\{{2R} = \sqrt{\left( {X_{e} - {R\;\sin\;\theta}} \right)^{2} + \left( {Y_{e} + {R\;\cos\;\theta} + R} \right)^{2}}} & (2) \\{\left\lbrack {{Expression}\mspace{14mu} 3} \right\rbrack\mspace{580mu}} & \; \\{R = \frac{\begin{matrix}{{X_{e}\sin\;\theta} - {Y_{e}\left( {1 + {\cos\;\theta}} \right)} -} \\\sqrt{\left\{ {{X_{e}\sin\;\theta} - {Y_{e}\left( {1 + {\cos\;\theta}} \right)}} \right\}^{2} - {2\left( {{\cos\;\theta} - 1} \right)\left( {X_{e}^{2} + Y_{e}^{2}} \right)}}\end{matrix}}{2\left( {{\cos\;\theta} - 1} \right)}} & (3)\end{matrix}$

However, when θ=0,

$\begin{matrix}{\left\lbrack {{Expression}\mspace{14mu} 4} \right\rbrack\mspace{580mu}} & \; \\{R = {- \frac{X_{e}^{2} + Y_{e}^{2}}{4\; Y_{e}}}} & (4)\end{matrix}$

From the state shown in FIG. 10(a) to the position of the crossing F7shown in FIG. 10(b) can be calculated by the above expressions.

The turning angles φ₁, and φ₂ of the S shape are calculated with theformula shown in FIG. 10(c) and the arc lengths b₁, and b₂ arecalculated with the following expressions.

$\begin{matrix}{\left\lbrack {{Expression}\mspace{14mu} 5} \right\rbrack\mspace{580mu}} & \; \\{\varphi_{1} = {2\;{\sin^{- 1}\left( \frac{\sqrt{X_{m}^{2} + Y_{m}^{2}}}{2R} \right)}}} & (5) \\{\left\lbrack {{Expression}\mspace{14mu} 6} \right\rbrack\mspace{580mu}} & \; \\{b_{1} = {2\; R\;{\sin^{- 1}\left( \frac{\sqrt{X_{m}^{2} + Y_{m}^{2}}}{2R} \right)}}} & (6) \\{\left\lbrack {{Expression}\mspace{14mu} 7} \right\rbrack\mspace{580mu}} & \; \\{\varphi_{2} = {2\;{\sin^{- 1}\left( \frac{\sqrt{\left( {X_{m} - X_{e}} \right)^{2} + \left( {Y_{m} - Y_{e}} \right)^{2}}}{2R} \right)}}} & (7) \\{\left\lbrack {{Expression}\mspace{14mu} 8} \right\rbrack\mspace{580mu}} & \; \\{b_{2} = {2\; R\;{\sin^{- 1}\left( \frac{\sqrt{\left( {X_{m} - X_{e}} \right)^{2} + \left( {Y_{m} - Y_{e}} \right)^{2}}}{2R} \right)}}} & (8)\end{matrix}$

FIG. 11 is a diagram explaining a method for generating aforward-direction path by S-shaped steering, and is a diagram explaininga generation method when the axis line E2 crosses with the X axis, whichis the axis line A2 at the current position A, behind the reachingposition E.

Here, the radius R of the common turning circles E1 and A1 having thesame radius is calculated to draw an S shape. Then, as long as a contactpoint of the circle is obtained, an S-shaped forward-direction path canbe generated by combining the arc of the turning circle A1 and the arcof the turning circle E1.

The radius of the common circle is obtained from the distance betweenthe center coordinates since the center coordinates of the circles areobtained.

$\begin{matrix}{\left\lbrack {{Expression}\mspace{14mu} 9} \right\rbrack\mspace{571mu}} & \; \\{{2R} = \sqrt{\left( {X_{e} - {R\;\sin\;\theta}} \right)^{2} + \left( {Y_{e} - {R\;\cos\;\theta} - R} \right)^{2}}} & (9) \\{\left\lbrack {{Expression}\mspace{14mu} 10} \right\rbrack\mspace{554mu}} & \; \\{R = \frac{\begin{matrix}{{- \left\{ {{X_{e}\sin\;\theta} - {Y_{e}\left( {1 + {\cos\;\theta}} \right)}} \right\}} -} \\\sqrt{\left\{ {{X_{e}\sin\;\theta} - {Y_{e}\left( {1 + {\cos\;\theta}} \right)}} \right\}^{2} - {2\left( {{\cos\;\theta} - 1} \right)\left( {X_{e}^{2} + Y_{e}^{2}} \right)}}\end{matrix}}{2\left( {{\cos\;\theta} - 1} \right)}} & (10)\end{matrix}$

The turning angles φ₁, and φ₂ of the S shape are calculated with theformula shown in FIG. 10(c) and the arc lengths b₁, and b₂ arecalculated with the following expressions.

$\begin{matrix}{\left\lbrack {{Expression}\mspace{14mu} 11} \right\rbrack\mspace{565mu}} & \; \\{\varphi_{1} = {2\;{\sin^{- 1}\left( \frac{\sqrt{X_{m}^{2} + Y_{m}^{2}}}{2R} \right)}}} & (11) \\{\left\lbrack {{Expression}\mspace{14mu} 12} \right\rbrack\mspace{565mu}} & \; \\{b_{1} = {2\; R\;{\sin^{- 1}\left( \frac{\sqrt{X_{m}^{2} + Y_{m}^{2}}}{2R} \right)}}} & (12) \\{\left\lbrack {{Expression}\mspace{14mu} 13} \right\rbrack\mspace{565mu}} & \; \\{\varphi_{2} = {2\;{\sin^{- 1}\left( \frac{\sqrt{\left( {X_{m} - X_{e}} \right)^{2} + \left( {Y_{m} - Y_{e}} \right)^{2}}}{2R} \right)}}} & (13) \\{\left\lbrack {{Expression}\mspace{14mu} 14} \right\rbrack\mspace{560mu}} & \; \\{b_{2} = {2\; R\;{\sin^{- 1}\left( \frac{\sqrt{\left( {X_{m} - X_{e}} \right)^{2} + \left( {Y_{m} - Y_{e}} \right)^{2}}}{2R} \right)}}} & (14)\end{matrix}$

FIG. 12 is a diagram explaining a method for generating aforward-direction path by S-shaped steering, and is a diagram explaininga generation method when the axis line E2 crosses with the X axis, whichis the axis line A2 at the current position A, behind the reachingposition E.

Here, the radius R of the common circles E1 and A1 having the sameradius is calculated to draw an S shape. Then, as long as a contactpoint of the circle is obtained, an S-shaped forward-direction path canbe generated by combining the arc of the turning circle A1 and the arcof the turning circle E1.

The radius of the common circle is obtained from the distance betweenthe center coordinates since the center coordinates of the circles areobtained.

$\begin{matrix}{\left\lbrack {{Expression}\mspace{14mu} 15} \right\rbrack\mspace{560mu}} & \; \\{{2R} = \sqrt{\left( {X_{e} - {R\;\sin\;\theta}} \right)^{2} + \left( {Y_{e} + {R\;\cos\;\theta} + R} \right)^{2}}} & (15) \\{\left\lbrack {{Expression}\mspace{14mu} 16} \right\rbrack\mspace{545mu}} & \; \\{R = \frac{\begin{matrix}{{X_{e}\sin\;\theta} - {Y_{e}\left( {1 + {\cos\;\theta}} \right)} -} \\\sqrt{\left\{ {{X_{e}\sin\;\theta} - {Y_{e}\left( {1 + {\cos\;\theta}} \right)}} \right\}^{2} - {2\left( {{\cos\;\theta} - 1} \right)\left( {X_{e}^{2} + Y_{e}^{2}} \right)}}\end{matrix}}{2\left( {{\cos\;\theta} - 1} \right)}} & (16)\end{matrix}$

The turning angles φ₁, and φ₂ of the S shape are calculated with theformula shown in FIG. 10(c) and the arc lengths b₁, and b₂ arecalculated with the following expressions.

$\begin{matrix}{\left\lbrack {{Expression}\mspace{14mu} 17} \right\rbrack\mspace{565mu}} & \; \\{\varphi_{1} = {2\;{\sin^{- 1}\left( \frac{\sqrt{X_{m}^{2} + Y_{m}^{2}}}{2R} \right)}}} & (17) \\{\left\lbrack {{Expression}\mspace{14mu} 18} \right\rbrack\mspace{565mu}} & \; \\{b_{1} = {2\; R\;{\sin^{- 1}\left( \frac{\sqrt{X_{m}^{2} + Y_{m}^{2}}}{2R} \right)}}} & (18) \\{\left\lbrack {{Expression}\mspace{14mu} 19} \right\rbrack\mspace{565mu}} & \; \\{\varphi_{2} = {2\;{\sin^{- 1}\left( \frac{\sqrt{\left( {X_{m} - X_{e}} \right)^{2} + \left( {Y_{m} - Y_{e}} \right)^{2}}}{2R} \right)}}} & (19) \\{\left\lbrack {{Expression}\mspace{14mu} 20} \right\rbrack\mspace{560mu}} & \; \\{b_{2} = {2\; R\;{\sin^{- 1}\left( \frac{\sqrt{\left( {X_{m} - X_{e}} \right)^{2} + \left( {Y_{m} - Y_{e}} \right)^{2}}}{2R} \right)}}} & (20)\end{matrix}$

<Parking-Path Setting Unit>

The parking-path setting unit 14 sets a parking path using theinformation on the backward-direction path from the target parkingposition to the connection candidate position selected by theforward-direction-path calculation unit 13 and the information on theforward-direction path from the own-vehicle position information to theconnection candidate position.

According to the present invention, since a backward-direction path iscalculated from a target parking position B, the closest connectioncandidate which is reachable from a current position A of an own vehicleis selected among a plurality of connection candidate positions D set onthe backward-direction path as a reaching position E, and a parking pathis set using the backward-direction path from the target parkingposition B to the reaching position E and a forward-direction path fromthe current position A of the own vehicle to the reaching position E, itis possible to calculate the parking path including turns for guidingthe own vehicle 21 to the target parking position B without depending onan initial position at which parking assist is started and on a vehicleposture, and to park the own vehicle 21 at a parking position desired bya driver with a proper vehicle posture.

The embodiment of the present invention has been described in detail,but the present invention is not limited to the above embodiment, anddesigns can be variously changed without departing from the spirit ofthe present invention described in the claims. For example, the aboveembodiment has been described in detail in order for the presentinvention to be easily understood, and is not necessarily limited tothose having all the described configurations. Furthermore, a part ofthe configuration of an embodiment can be replaced with theconfiguration of another embodiment, and the configuration of anembodiment can be added to the configuration of another embodiment.Moreover, other configurations can be added, deleted, or replaced withrespect to a part of the configuration of each embodiment.

REFERENCE SIGNS LIST

-   1 Parking assist device-   11 Backward-direction-path calculation unit-   12 Connection-candidate-position storage unit-   13 Forward-direction-path calculation unit-   14 Parking-path setting unit-   15 Operation input unit-   16 Path display unit-   21 Own vehicle-   22 Reference point-   31 Parking frame-   32, 33 Obstacle-   A Current position-   B Target parking position-   C Reachable limit position-   D Connection candidate position-   E Reaching position-   G Passage-   PLn Connection candidate line

The invention claimed is:
 1. A parking assist device that calculates aparking path from a current position of an own vehicle to a targetparking position, the parking assist device comprising: a sensor; aninput; and a processor that is communicatively coupled to the sensor andthe input, wherein the processor is configured to: determine, using thesensor, the current position of the own vehicle; receive, using theinput, the target parking position; calculate a backward-direction pathfor taking the own vehicle out from the target parking position based onconstraint conditions of a parking space and an own-vehicle behavior anda number of turns of the own vehicle; set a plurality of connectioncandidate positions on the backward-direction path; sequentiallycalculate paths respectively leading to the plurality of connectioncandidate positions from the current position of the own vehicle basedon the number of turns of the own vehicle and the current position ofthe own vehicle; select a connection candidate position to which a pathhaving a shortest moving distance from the current position of the ownvehicle leads; determine whether the own vehicle collides with anobstacle; change a gear of the own vehicle to change a moving directionof the own vehicle between a forward direction of the own vehicle and abackward direction; determine the path leading to the selectedconnection candidate position as a forward-direction path; and set theparking path by combining the backward-direction path and theforward-direction path such that a steering direction of the own vehicleis changed.
 2. The parking assist device according to claim 1, whereinthe processor is further configured to: determine whether the ownvehicle can reach each of the connection candidate positions from thecurrent position of the own vehicle by one-side steering or by S-shapedsteering; and select the connection candidate position by determiningthat the own vehicle can reach the connection candidate position fromthe current position of the own vehicle by one-side steering or byS-shaped steering.
 3. The parking assist device according to claim 1,wherein the processor is further configured to: calculate, in a case ofbackward parallel parking, the forward path for the own vehicle to reacha reachable limit position with respect to a front obstacle by steeringto either the left or the right and moving forward, and a backward pathfor the own vehicle to reach a reachable limit position with respect toa rear obstacle by straightening the front wheels with respect to theown vehicle and moving backward.
 4. The parking assist device accordingto claim 1, wherein the processor is further configured to: calculate,in a case of forward parallel parking, a backward path for the ownvehicle to reach a reachable limit position with respect to a rearobstacle by steering to either the left or the right and movingbackward, and a forward path for the own vehicle to reach a reachablelimit position with respect to a front obstacle by straightening thefront wheels with respect to the own vehicle and moving forward.
 5. Theparking assist device according to claim 1, wherein the processor isfurther configured to: determine whether the own vehicle can reach eachof the connection candidate positions from the current position of theown vehicle by one-side steering; select the connection candidateposition by determining that the own vehicle can reach the connectioncandidate position from the current position of the own vehicle byone-side steering; and select the connection candidate position when anaxis line of the own vehicle at the current position of the own vehicleand the axis line of the own vehicle at a reaching position after takingout from the target parking position cross, a turning circle at thecurrent position and the axis line at the reaching position do notcross, and the axis line at the current position and a turning circle atthe reaching position do not cross, the axis line of the own vehiclepassing at an center of the own vehicle and extending in a longitudinaldirection of the own vehicle.